This invention relates in general to a cascade type thrust reverser for aircraft turbine engines and, more particularly, to a thrust reverser having blocker doors adapted to partially block fan flow and having cascade sets to reverse flow.
Modern aircraft fan jet engines have a fan cowl or shroud surrounding the fan portion of the engine and spaced outwardly from the core engine cowl to define an annular passage or duct for flow of fan air rearwardly from the outer portion of an enlarged axial flow fan. In this type of engine, a large proportion of the total thrust is developed by the reaction to the air driven rearwardly by the fan and the balance results from ejection of the exhaust gas stream from the engine.
Aircraft using gas turbine engines tend to have high landing speeds, placing great stress on wheel braking systems and requiring very long runways. To reduce this braking requirement and permit use of shorter runways, means are now provided in such engines for reversing a major portion of engine thrust during the landing roll. Many different types of thrust reversers have been designed, of varying effectiveness.
With fan-jet engines, it is possible to block and reverse substantially all of the fan flow without excessive stress on the system, since a large part of the core flow continues through the engine. In some cases, sufficient reverse flow can be obtained by blocking only a substantial portion of the fan flow.
One type of thrust reverser often used in non-fan type turbine engines, uses a pair of large sturdy clam-shell like blocker doors which swing directly behind the jet exit nozzle and diverge forwardly to reverse thrust. This system must be very heavy and strong. Very complex and sturdy actuators are required for this system.
Another design uses pivotable doors lying in opening in the sidewall of the shroud or fan cowl which pivot outwardly while a second set of doors pivot inwardly to block flow of air through the duct and direct it to the outwardly extending doors which direct air flow rearwardly. Typical of these is the system disclosed by Ellis in U.S. Pat. No. 3,612,401. These systems, while useful in fan-jet engines, tend to be heavy and mechanically complex.
Yet another design uses a plurality of pivotable doors located in openings arranged radially around the fan shroud. Each door pivots so that one inner end nearly contacts the engine cowl to block air flow through the annular duct while the other end extends outside the fan cowl in a direction to direct air forwardly. Typical of these the systems disclosed by Maison et al in U.S. Pat. No. 3,605,411 and Fournier et al in U.S. Pat. No. 4,485,970.
Still another type of thrust reverser uses cascade sets positioned in the sidewalls of the fan cowl with a translating system for uncovering the cascades to direct air flow through the guide vanes of the cascades, which turn the airflow in a forward direction. Typical cascade type reversers include those disclosed by Montgomery in U.S. Pat. No. 4,145,877 and Hom et al in U.S. Pat. No. 3,500,646. These systems are often mechanically simpler than others, since only a small internal blocker door set is needed and the cascade set can be rigidly secured to the fan cowl, thereby resulting in fewer separate moving parts. However, it is generally necessary that at least a portion of the actuating devices for uncovering the cascades and for moving the blocker doors extend into the air stream to the engine cowl during normal engine operation. This increases drag and is wasteful of fuel.
Thus, there is a continuing need for improved thrust reverser systems for fan-jet engines which are mechanically sturdy while being light in weight and avoiding added drag within the fan air flow.